A 3-methylbutene-1 polymer (sometimes called a 3-methyl-1-butene polymer) is among polyolefins having the highest melting point, stiffness and strength and, in addition to excellent electrical insulation properties, nonhygroscopicity and chemical resistance which are characteristics of polyolefin resins, exhibits high heat resistance. Thus, the 3-methylbutene-1 polymer is expected to find many uses.
However, much higher stiffness, strength and heat distortion temperature are needed for some of electrical appliances, building materials, car parts, mechanical parts, and so forth. In these applications, the 3-methylbutene-1 polymer is not sufficiently satisfactory.
As a result of extensive investigations to develop a 3-methylbutene-1 polymer composition which can be used in the above described fields requiring higher stiffness, strength and heat distortion temperature, it has been found that the object can be attained by adding a specific amount of a fibrous material to a specific 3-methylbutene-1 polymer.